Display screens are the primary interface for displaying information from a computer. Display screens are limited in size, thus presenting a challenge to graphical user interface design, particularly when large amounts of information are to be displayed. This problem is normally referred to as the “screen real estate problem”.
Well-known solutions to this problem include panning, zooming, scrolling or combinations thereof. While these solutions are suitable for a large number of visual display applications, these solutions become less effective where sections of the visual information are spatially related, such as maps, three-dimensional representations, newspapers and such like. In this type of information display, panning, zooming and/or scrolling is not as effective as much of the context of the panned, zoomed or scrolled display is hidden.
A recent solution to this problem is the application of “detail-in-context” presentation techniques. Detail-in-context is the magnification of a particular region of interest (the “focal region” or “detail”) in a data presentation while preserving visibility of the surrounding information (the “context”). This technique has applicability to the display of large surface area media, such as maps, on computer screens of variable size including graphics workstations, laptop computers, personal digital assistants (“PDAs”), and cell phones.
In the detail-in-context discourse, differentiation is often made between the terms “representation” and “presentation”. A representation is a formal system, or mapping, for specifying raw information or data that is stored in a computer or data processing system. For example, a digital map of a city is a representation of raw data including street names and the relative geographic location of streets and utilities. Such a representation may be displayed visually on a computer screen or printed on paper. On the other hand, a presentation is a spatial organization of a given representation that is appropriate for the task at hand. Thus, a presentation of a representation organizes such things as the point of view and the relative emphasis of different parts or regions of the representation. For example, a digital map of a city may be presented with a region magnified to reveal street names.
In general, a detail-in-context presentation may be considered as a distorted view (or distortion) of a portion of the original representation where the distortion is the result of the application of a “lens” like distortion function to the original representation. A detailed review of various detail-in-context presentation techniques such as Elastic Presentation Space may be found in a publication by Marianne S. T. Carpendale, entitled “A Framework for Elastic Presentation Space” (Carpendale, Marianne S. T., A Framework for Elastic Presentation Space (Burnaby, British Columbia: Simon Fraser University, 1999)), and incorporated herein by reference.
In general, detail-in-context data presentations are characterized by magnification of areas of an image where detail is desired, in combination with compression of a restricted range of areas of the remaining information (i.e. the context), the result typically giving the appearance of a lens having been applied to the display surface. Using the techniques described by Carpendale, points in a representation are displaced in three dimensions and a perspective projection is used to display the points on a two-dimensional presentation display. Thus, when a lens is applied to a two-dimensional continuous surface representation, for example, the resulting presentation appears to be three-dimensional. In other words, the lens transformation appears to have stretched the continuous surface in a third dimension.
One shortcoming of these detail-in-context presentation systems is that the rendering of a raster image which has under-gone a distortion through the application of one or more lenses (e.g. pyramid lenses) can be time consuming. Both the CPU and input/output systems of the detail-in-context presentation system can be taxed when performing such a rendering. Past techniques for rendering these images have usually involved texturing the raster image upon a three-dimensional triangulated surface. This technique can provide fast results, especially when combined with the use of accelerated three-dimensional rendering hardware, but rendering can be slow when no such hardware is present. In addition, the result is only an approximation of the true distortion of the lens with accuracy being limited by the coarseness of the triangulated mesh. It would desirable to have a method for rendering an accurately distorted raster image quickly and without the need for specialized rendering hardware.
A need therefore exists for the fast and effective display of detail-in-context lens presentations in detail-in-context presentation systems. Consequently, it is an object of the present invention to obviate or mitigate at least some of the above mentioned disadvantages.